Gaseous fuels are frequently liquefied to reduce the volume they occupy during transport and storage. Typically, the gas is liquefied at or in the vicinity of its production site, it is then stored and/or shipped in containers to its point of use, and there it is gasified again before it is distributed to users. There are a variety of such gases, however, by far the most common gas is natural gas which includes methane as its major component. Although the present invention is applicable to a number of gases, as is further discussed below, all such gases will hereinafter be sometimes collectively referred to as "natural gas," a definition intended to include all gases which have at least a methane component.
As the use of liquefied fuels continues to grow, its potential hazards to humans and property are immense because of the very large energy that is concentrated in such liquefied gases. The greatest danger in connection with the storage, handling and shipment of liquefied natural gas is posed by potential spills due to collisions, rupture of containers or similar accidents. In such instances the liquid natural gas (LNG) escapes onto the ground or the water surface where it rapidly evaporates into gas clouds which can cover very large surface areas and which can move over relatively large distances before they are sufficiently diluted so as to preclude their explosion. Before such dilution even a minor spark or flame can set off an explosion which can release energy equivalent to up to thousands of tons of TNT.
This danger posed by LNG has of course been recognized for some time. To alleviate the rapid outflow of LNG if its container should be ruptured, it has previously been proposed to gel the LNG. U.S. Pat. No. 4,011,730 discloses and claims a method by which LNG is gelled through mixing relatively small amounts of finely divided solid particles of water or methyl alcohol with the LNG. In accordance with the method disclosed in that patent the gelling agent, say steam, is injected into the LNG via a tube submerged in the LNG. Steam may be directly injected or it may first be entrained in a carrier gas such as helium or methane.
To effectively gel the LNG the steam and the resulting solid particles must be relatively uniformly dispersed throughout the LNG pool. Because of the extremely low temperatures of LNG this is not always an easy task since the solid particles tend to agglomerate around the tube and can also cause it to become plugged.